1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus. More particularly, the present invention relates to a developer having a development roller with an improved rotational structure, and an electrophotographic image forming apparatus including the developer.
2. Description of the Related Art
Generally, image forming apparatuses, such as laser printers and digital copying machines, are devices that scan light to a photosensitive medium that is charged at a predetermined potential to form an electrostatic latent image on an outer peripheral surface of the photosensitive medium. A developing agent, such as toner, is applied to the electrostatic latent image to develop the latent image into a visible image. The image is transferred and fixed to a sheet of paper to print the image. An electrophotographic image forming apparatus includes a developer that is detachably mounted inside a body. The developer includes the photosensitive medium, which has the electrostatic latent image formed on the outer peripheral surface thereof, and a development roller, which conveys the toner to the outer peripheral surface of the photosensitive medium. The developer is replaced with a new developer when the toner contained therein is depleted.
Power for rotating the photosensitive medium or the development roller during the printing process is transferred from a motor disposed inside the body. If the developer is mounted inside the body for the power transfer, the motor and the developer are coupled to each other using predetermined coupling means. FIG. 1 is an exploded perspective view of coupling means for coupling the developer to the motor in a conventional electrophotographic image forming apparatus.
Referring to FIG. 1, the coupling means includes a triangular protrusion 11, which extends in a longitudinal direction of a photosensitive drum 5 from a front end portion of a rotary shaft 10 of the photosensitive drum 5. A power transfer shaft 20 that is rotatably connected to a motor (not shown) has a triangular groove 22 facing the triangular protrusion 11. The power transfer shaft 20 is operatively connected to a door (not shown) of the image forming apparatus that is opened to allow a developer including the photosensitive drum 5 to be installed in or removed from the image forming apparatus therethrough, such that the power transfer shaft 20 moves forward and backward in a direction indicated by the arrow when the door is opened and closed. The rotary shaft 10 of the photosensitive drum 5 is inserted into an aperture 17 formed in a developer frame 15 such that the photosensitive drum 5 is rotatably mounted to the developer frame 15. Accordingly, the triangular protrusion 11 is exposed outside of the developer frame 15.
If the door is opened to mount the developer in a body of the image forming apparatus, the power transfer shaft 20 moves rearwardly. If the developer is inserted in the body of the image forming apparatus and the door is closed, the power transfer shaft 20 moves forwardly, thereby inserting the triangular protrusion 11 of the photosensitive drum 5 in the triangular groove 11 such that the motor inside the body is connected to the photosensitive drum 5 inside the developer. Consequently, if the motor rotates according to a printing order, the power of the motor is transferred to the photosensitive drum 5 to rotate the photosensitive drum 5.
Alternatively, a gear portion 7 is disposed on an outer peripheral surface of a longitudinal end of the photosensitive drum 5. A corresponding gear portion (not shown) meshing with the gear portion 7 of the photosensitive drum 5 is disposed on an outer peripheral surface of a longitudinal end of each of a development roller, a supply roller, and an agitator inside the developer. Accordingly, if the photosensitive drum 5 rotates, the development roller, the supply roller, and the agitator rotate subsequently.
As described above, since the power transfer shaft 20 is operatively connected to the door and thus moves forwardly and rearwardly when the door is opened and closed, the power transfer shaft 20 has a complex structure and requires many components, thereby increasing manufacturing costs and increasing the difficulty of manufacturing the power transfer shaft 20. The rotational speed of the development roller, which is geared with the photosensitive drum to rotate, may vary according to a degree to which teeth of the gear portion 7 of the photosensitive drum 5 and teeth of the gear portion of the development roller are processed. This may result in a jittery printed image.
Further, the development roller engaged with the photosensitive drum 5 is forced to be farther from or closer to the photosensitive drum 5 as the photosensitive drum 5 rotates. Accordingly, a gap between an outer peripheral surface of the photosensitive drum 5 and an outer peripheral surface of the development roller may be different from a preset value, which adversely affects the quality of the printed image.
Accordingly, there is a need for a developer having an improved rotational structure for an electrophotographic image forming apparatus to improve print quality.